Rare earth and group 4 catalysts for ambient conversion of dinitrogen to secondary silylamines

Abstract

Catalysts and methods for dinitrogen conversion to secondary silyamines or ammonia (N2RR) are provided. The catalysts are a metalacyclic platform characterized by a pocket with tunable dimensions and conditions. The catalysts show dramatically improved N2RR activity compared to previously reported early d-block catalysts. The tetraphenolate-supported bimetallic lanthanide or group IV metal complex undergoes multiple two-electron reductions, the last of which leads to the reductive activation of dinitrogen. The inclusion of a weak acid and silyl electrophiles during the reduction enables the catalytic conversion of N2 to purely secondary amines.

What is claimed is: 
     
         1 . A method for the conversion of dinitrogen to secondary amines, the method comprising:
 (a) providing a catalyst of a tetravalent metalacyclic complex of a metal selected from the group of lanthanide metals and group IV metals, and meta-phenyl-bridged tetraphenolate ligands;   (b) providing dinitrogen source, a group 1 metal reductant, and an electrophile;   (c) mixing the catalyst and an excess of reductant in tetrahydrofuran (THF) and dinitrogen atmosphere to produce a first mixture;   (d) adding the electrophile to the first mixture to produce a second mixture;   (e) mixing the second mixture to complete the reaction; and   (f) collecting the reaction products.   
     
     
         2 . The method of  claim 1 , wherein said lanthanide metals are selected from the group consisting of lanthanum (La), cerium (Ce) neodymium (Nd) and samarium (Sm). 
     
     
         3 . The method of  claim 1 , wherein said group IV metals are selected from the group consisting of titanium (Ti) and zirconium (Zr). 
     
     
         4 . The method of  claim 1 , wherein said meta-phenyl-bridged tetraphenolate ligands of said complex are selected from the group consisting of [{2-(OC 6 H 2 -2-tBu, 4-Me) 2 CH}-1,3-C 6 H 4 ] and mTP. 
     
     
         5 . The method of  claim 1 , wherein said catalyst complex comprises a 2:2 metal-to-ligand complex (M 2 L 2 ). 
     
     
         6 . The method of  claim 1 , wherein said catalyst complex comprises a 2:1 metal-to ligand complex (M 2 L 1 ). 
     
     
         7 . The method of  claim 1 , wherein said metal reductant is a metal selected from the group of metals consisting of sodium (Na), potassium (K) and rubidium (Rb). 
     
     
         8 . The method of  claim 1 , wherein said electrophile comprises ClSiMe 3 . 
     
     
         9 . The method of  claim 1 , wherein said nitrogen source comprises atmospheric nitrogen at room temperature and pressure. 
     
     
         10 . The method of  claim 1 , further comprising:
 adding a proton source to the first mixture after the addition of the electrophile to produce the second mixture.   
     
     
         11 . The method of  claim 10 , wherein the proton source comprises a weak acid. 
     
     
         12 . The method of  claim 11 , wherein the weak acid comprises [HNEt 3 ][BPh 4 ]. 
     
     
         13 . The method of  claim 1 , further comprising:
 treating the collected reaction products with hydrochloric acid to produce ammonia.   
     
     
         14 . The method of  claim 1 , further comprising:
 controlling the selection of the catalyst metal, complex dimensions and the composition of the reductant and electrophile to promote reaction products.   
     
     
         15 . A catalyst composition comprising:
 a tetravalent metalacyclic complex of a metal selected from the group of group IV metals and at least one metal-tetraphenol (H 4 L) ligand, where L=[{2-(OC 6 H 2 -2-tBu, 4-Me) 2 CH}-1,3-C 6 H 4 ].   
     
     
         16 . The catalyst composition of  claim 15 , wherein said complex comprises a 2:2 metal-to-ligand complex (M 2 L 2 ). 
     
     
         17 . The catalyst composition of  claim 15 , wherein said complex comprises a 2:1 metal-to ligand complex M 2 L 1 . 
     
     
         18 . The catalyst composition of  claim 15 , wherein said metal is a metal selected from the group consisting of Ti and Zr. 
     
     
         19 . A catalyst composition comprising:
 a tetravalent metalacyclic complex of a metal selected from the group of lanthanide metals and at least one meta-phenyl-bridged tetraphenolate ligand L=mTP.   
     
     
         20 . The catalyst of  claim 19 , wherein said lanthanide metals are selected from the group consisting of lanthanum (La), cerium (Ce) neodymium (Nd) and samarium (Sm).